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Topic Title: New 3 phase installation
Topic Summary: A little advice needed.
Created On: 17 February 2013 06:54 AM
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 17 February 2013 06:54 AM
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MarkClive

Posts: 3
Joined: 17 February 2013

I only do domestic normally but a friend has asked me to wire up some new industrial units for him and I have a few concerns/questions.

The distribution boards are standard 6 ways with 125A incomers, the distance to the new meter cupboard is less than 2 meters so I will be running 35mm tails.

The issue I have is that he has told me the supply he has requested is only 45KVA. Now if my memory serves me correctly amps per phase would be

KVA x 1000 / (line to line voltage x root 3)

which is

45000 / (400 x root 3) = about 65A.

Assuming the above is correct will I get a problem when EDF come to install the new meters? I am worried about a conversation along the lines of ... your maximum potential load is double what you have asked for and we are not connecting it.

Like I say I haven't installed 3 phase before and I would rather look like a newbie on here than have to fix it on site later. Any advice would be gratefully received.

Thanks All
 17 February 2013 08:53 AM
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statter

Posts: 118
Joined: 06 February 2013

I think the main issue will be whether your tails will fit into the meter. Not all of the smaller meters will take 35mm2 tails.

This isn't an EDF matter as the MOP will fit the meter.
The cutout fuse will limit what you will get, they will probably fit a 100A fuse as standard.
 17 February 2013 10:45 AM
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UKPN

Posts: 452
Joined: 17 January 2012

the issue with this job is not the load (60 amps per phase) but the m/sw
size.
with a 125 we would expect 35sqmms even with 100amp fuses,

Regards
 17 February 2013 10:47 AM
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alancapon

Posts: 5699
Joined: 27 December 2005

It all depends. If your friend has requested a 45kVA supply, this could be met with 60A or 80A fuses in the cutout (depending on the nominal voltage that the DNO / Meter Operator use for the calculation). You may well have trouble with the tails though, as 100A/phase is usually the limit for "whole current metering" where the load flows through the meter, rather than a set of CTs. It is therefore not unusual to discover that a meter tail larger than 25mm² will not fit.

Regards,

Alan.
 17 February 2013 11:17 AM
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aligarjon

Posts: 2735
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If you only want 65amps why don't you just use 25mm tails ?

Gary

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 17 February 2013 12:29 PM
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slittle

Posts: 3374
Joined: 22 November 2007

I'd go with 25mm tails. Most if not all of the main switches are rated at 125A now.

Not going to be an issue because as Alan has said at that sort of supply size you will only get a maximum of 100A fuses because the metering will be whole current and not CT. I've done several jobs where we've had to fit replacement tails because the MOP has wanted to fit a replacement meter and the existing tails @ 35mm wouldn't fit it.

UKPN, do you want to think about your post. The mainswitch won't be providing any protection in that installation only isolation so it wouldn't matter what size switch it was. My chart from your employer tells me 100A fuses / 25mm tails unless of course they've moved the goalposts, but then it's not really a UKPN issue as the MOP makes the connections these days.

Stu
 17 February 2013 08:51 PM
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UKPN

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in this situation, we must take into account the 125 isolator and possible
large power cut out terminals.
in that case, 35 is a better fit, and all meters fit 35s.
after all, you wouldnt fit 16mms would you, although the load is only 60

Regards
 18 February 2013 09:16 AM
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MrP

Posts: 815
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Doesn't matter if it's a 125A switch disconnector or a 600A switch disconnector the switch disconnector offers no overload protection it's a switch
100A supply 25mm tails
Load 60A 16mm tails would be adequate its only a local requirement from the Electricity Board that 25mm tails be fitted.
Would you fit 25mm tails for a 2way consumer unit with a 125 switch disconector supplying a shower or cooker circuit 10mm or 16mm tails I think
MrP Still going home in ten days
 18 February 2013 09:35 PM
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slittle

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Originally posted by: UKPN

in this situation, we must take into account the 125 isolator and possible

large power cut out terminals.

in that case, 35 is a better fit, and all meters fit 35s.

after all, you wouldnt fit 16mms would you, although the load is only 60



Regards


But the cutout size isn't our problem if it's a whole current supply. That's between you and the MOP. If it was my job you would be getting 25mm tails and I'd be asking for a 70kva supply from UKPN Connections.

I don't do "small supplies" in my world if you want a 3 phase connection unless the DNO have a really good reason against it, you get a 70KVA one.

Farming always grows so there is little point in asking for anything less.

Stu
 19 February 2013 08:13 AM
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tomgunn

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worst comes to worse and the amps are ok then its trim the tails to fit the meter or use smaller tails.

Tom

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I can resist anything..... except temptation! ( Karl Gunn ).
 19 February 2013 06:58 PM
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OMS

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Originally posted by: UKPN

in this situation, we must take into account the 125 isolator and possible

large power cut out terminals.

in that case, 35 is a better fit, and all meters fit 35s.

after all, you wouldnt fit 16mms would you, although the load is only 60

Regards


If I'd asked for a 45kVA supply, for sure I'd fit 16mm2 by design.

If I thought the DNO was going to give me 80A or 100A fuses as a default, then I'd probably go with 25mm2 as a reasonable DNO suggestion for a typoical 100A service position.

What I wouldn't be doing is effectively doubling the conductor CSA from 16mm2 to 35mm2 just because I'd used a standard TP&N Type B dist board with a 125A disconnector.

It would be absolutely nothing to do with the supplier or meter operator -you lot would just need to get on with ESQCR Reg 24 and give me my supply and protection to my tails based on my decalared capacity in the connection agreement.

35mm2 tails on a small industrial shed with 63A supply fuses - what a joke.

Would you be wanting an increase in the earthing conductor and bonding conductor as well - just in case like

Regards

OMS

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 20 February 2013 07:25 AM
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MarkClive

Posts: 3
Joined: 17 February 2013

Thanks for all the replies.

I was missing the obvious with the incoming switch. It has been highlighted here that it is just an isolation device and offers no overload protection, I had that wrong in my mind for some reason.

I am doing the job next week and I will fit 25mm tails. They will be fine for the 45 KVA supply that the client requested and if they actually fit a 70 KVA supply they will be fine for that as well.

Thanks again for the help it is much appreciated.
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